Multiple sensors are known by people in the field of pressure sensing technology. Particularly, pressure sensor based on semiconductor technology is well known by people. Pressure sensor chip is composed of a silicon substrate and an epitaxial layer growing on the silicon substrate, wherein an elastic film is formed on the silicon substrate through MEMS (micro electro mechanical system) technology. If a pressure is applied on the elastic film, the elastic film will be bent at a certain degree according to the intensity of pressure. Sensitive components formed by deposition or ion implantation may be bent due to deformation of the film. The sensitive components have the piezoresistive effect, so, they have resistance variation, and the resistance variation are converted into a voltage and output through a Wheatstone bridge composed of the sensitive components.
In the relevant technical fields, a pressure sensor for measuring target fluid pressure is introduced in the patent (No. US2012/0144923A1). The introduced pressure sensor comprises a housing, a sensor chip, a data processing chip, and a cover plate for sealing. Two separation inlet holes are set on one side of the same plane on the upper part of the housing, one is used for leading the measured fluid into the inner cavity of the housing, and the other one is in communication with the air. Particularly, the pressure of the lead-in measured fluid acts on the front of the sensor chip; however, the lead-in air pressure acts on the back cavity of the sensor chip. In addition, the data processing chip set at one side of the sensor chip is in mutual connection with the sensor in a lead bonding manner. At last, the inner cavity of the housing is sealed through the cover plate.
However, through the structure of the pressure sensor introduced in the above-mentioned patent, the measured fluid enters the inner cavity of the housing through the fluid lead-in hole and directly touches the front of sensor chip, so the circuit set on the surface of sensor will be affected seriously by the disturbance of measured fluid, even reliability and long-term stability of the sensor will be reduced. Further, the air lead-in hole and pressure lead-in hole of the sensor in the above-mentioned patent are set to be convex cylindrical holes separated from each other, and this structure is easy to cause increase of sensor size and reduction of intensity. If there is a large distance between the two holes, it shows that plan view size of the sensor in the XY direction is large; if there is a small distance between the two holes, it shows that long air inlet hole shall be set to increase the size in the Z distance of sensor, as a result, torsional rigidity of the pressure inlet part (i.e. the pressure inlet part 1a in FIG. 2) on the housing is reduced. Further, the data processing circuit is not integrated in the pressure sensor chip, so the sensor will be more complex in structure and higher in cost. Further, it is more likely to cause leakage due to poor sealing when the measured fluid is put into the housing.
Content
For overcoming defects existing in the prior art, the present disclosure provides a pressure sensor and a manufacturing method thereof. The pressure sensor is featured with high reliability, good long-term stability, small integrated chip size and high accuracy. The technical scheme is as follows:
A pressure sensor, comprising a housing, an air lead-in hole, a pressure lead-in hole, an inner cavity, a sensor chip, a lead frame and a cover plate; the housing, the pressure lead-in holes and the inner cavity are integrally formed by means of an injection molding process; one end of the air lead-in hole is in communication with the inner cavity of the housing, and the other end of the air lead-in hole is in communication with the air; the pressure lead-in hole is perpendicularly disposed at the center of the upper surface of the housing, two steps are disposed on the upper surface of the inner cavity, and a horizontal surface-mounted device surface is disposed on the of the steps; the sensor chip is integrated with a data processing circuit and adhered on the horizontal upper surface of the inner cavity of the housing in an inverted manner by means of adhesives; the center of the sensor chip is aligned with the center of the pressure lead-in hole, and lower end of the pressure lead-in holes is in communication with the cavity of the sensor chip; the lead frame is tightly adhered with the housing in the process of injection molding curing of the housing, and a bonding pad of the lead frame is disposed on each of the steps in the inner cavity; the sensor chip and the lead frame are electrically connected in a gold wire bonding manner, and the cover plate is adhered with the bottom of the housing by means of adhesives.
In the pressure sensor, the air lead-in hole is used for leading air pressure into the inner cavity of the housing; the pressure lead-in hole is used for leading the measured fluid, and the pressure of the measured fluid acts on the back cavity of the sensor chip; the sensor chip is used for measuring the pressure of the fluid to the air; particularly, the data processing circuit is integrated on the chip, and the cover plate is used for sealing the inner cavity of the housing.
Preferably, in the pressure sensor, the housing comprises a cavity part, a tubular pressure inlet part extending from the surface of housing to outside, and an air inlet part coaxial with the pressure inlet part. Particularly, a step is set between the top of air inlet part and the top of pressure inlet part. Further particularly, the air lead-in hole is composed of multiple through holes, which are distributed in a circular array form.
Preferably, the housing comprises a cavity part and a tubular pressure inlet part extending from the surface of housing to outside, and the air lead-in hole of the sensor is set at the side of the housing, which is vertical to the air lead-in hole.
Preferably, the housing comprises a cavity part and a tubular pressure inlet part extending from the surface of housing to outside, and the air lead-in hole is integrated on the upper surface of the housing and connected with the inner cavity of the housing.
Preferably, the cover plate and the air lead-in hole are integrally formed by means of the injection molding process; the sensor chip is adhered on the surface-mounted device surface by means of adhesives, and then coated with sealant.
Further particularly, the housing comprises a pressure inlet part, an air inlet part and a cavity part; the air lead-in hole is composed of two parts which are a vertical hole and a horizontal hole; the lower end of the vertical hole is in communication with the inner cavity, the upper end of the vertical hole is ended at the interior of housing; one end of the horizontal hole is in communication with the air, and the other end of the horizontal hole is in communication with the vertical hole.
A manufacturing method for pressure sensor, comprising the following steps:
Step 1: making a lead frame: the lead frame is made of tin bronze material, and both the pin and bonding pad in the lead frame are nickeled for 2 microns and gilded for 0.05 microns;
Step 2: the housing of sensor, the air lead-in hole, the pressure lead-in holes and the inner cavity are formed by means of an injection molding process; the housing and the cover plate are made of PBT+30% GF; while the housing is injected, the lead frame is tightly adhered with the housing through this process, a bonding pad of the lead frame is disposed on each of the steps in the inner cavity, and then a pin of the lead frame is bent;
Step 3: the sensor chip is adhered in the center of surface-mounted device surface in the housing in an inverted manner to make the cavity of the sensor chip be in communication with the pressure lead-in hole, wherein the sensor chip is tightly adhered with the surface-mounted device surface by means of adhesives, and then they are dried at the temperature of 150° C. for 30 min, so as to make the sensor chip compactly and firmly be communication with the surface-mounted device surface;
Step 4: the sensor chip and the lead frame are electrically connected in a gold wire bonding manner;
Step 5: the cover plate is adhered with the bottom of the housing cavity by means of adhesives, and they are dried at the temperature of 150° C. for 30 min.
Beneficial effects of the present disclosure: the difference between the data processing chip and sensor chip used in the prior art at the same time is that the data processing circuit in the pressure sensor of the invention is integrated in the sensor chip, as a result, mutual electrical connection between the chips is reduced, so as to greatly reduce the possibility of making the sensor disabled in the electrical connection aspect. In the other aspect, the measured fluid makes its pressure act on the back cavity of the sensor chip directly through the pressure lead-in hole in the pressure sensor of the invention, so it just needs to ensure effective sealing of the sensor chip and the surface-mounted device surface, so as to reduce the sealing area and leakage risk of the sensor; meanwhile, this structure bearing the pressure on the back is capable of preventing adverse effect for electrical connection of the fluid disturbance for the sensor. In addition, the air lead-in hole is connected with the inner cavity of the housing to make the air pressure act on the front of the sensor chip, so it needs to ensure accuracy of the sensor.
In the first exemplary embodiment, the air lead-in hole of the sensor is composed of multiple through holes, which are distributed in circular array form and coaxial with the air lead-in hole, so that the structure of sensor is simplified and it is beneficial for reducing the size of sensor. A step is set between the upper surface of pressure lead-in hole and the upper surface of the air lead-in hole, to facilitate positioning during assembly with the external pipe, and to prevent the air lead-in hole from being jammed by the pipe. In the second exemplary embodiment, the air lead-in hole is set at the side of the housing, and this structure is capable of effectively reducing the possibility that the external pollutant enters into the cavity, without influence on potting. In the third exemplary embodiment, the air lead-in hole is integrated on the upper surface of the housing, and the structure of structure is further simplified. In the fourth exemplary embodiment, the air lead-in hole is set in the cover plate of the sensor, and this structure is beneficial for using the pouring sealant for performing potting protection for the sensor chip, so as to avoid the pollution by the air. In the fifth exemplary embodiment, the air lead-in hole is composed of two parts, and this structure is capable of effectively preventing the external pollutant from entering into the inner cavity of the housing and preventing the air lead-in hole from being jammed by the pipe during assembly; in addition, the step on the upper part of the air lead-in hole is capable of providing positioning for the pipe assembly.